GAITHERSBURG, Md. (AP) ¿ Federal health advisers on Wednesday rejected an implant from Zimmer Holdings saying it's unclear how effective or safe the device would be for treating a painful spinal condition.

The Food and Drug Administration's panel of outside experts voted 5-1 that Zimmer's titanium Dynesys implant should not be approved to restabilize the spine.

The FDA is not required to follow the group's recommendation, though it often does.

The group of spinal surgeons said Zimmer studies have not clearly shown which patients would benefit from the implant.

"There were conflicting results without adequate explanation," said Dr. John Kirkpatrick of the University of Florida College of Medicine. "I don't think they've put adequate thought into why they found what they did."

The group also had concerns about wear and tear on the device over time.

"I think the panel generally believes this is reasonably safe, however the long-term safety remains to be seen," said panel chair Dr. John Kelly of the University of Pennsylvania.

Warsaw, Ind.-based Zimmer Holdings Inc. has asked the FDA to approve its implant to re-stabilize the spine when vertebrae have slipped loose, causing leg pain and muscle weakness. The device would be used instead of spinal fusion, a surgical procedure that involves fusing vertebrae together, but can often carry complications.

Mason Macenski, Zimmer's director of clinical affairs, concluded his presentation saying the company's data "demonstrated a reasonable assurance of safety and effectiveness," though that wasn't enough to persuade the panel.

A Zimmer study of the device met its goal, showing results at least as good as spinal fusion using the company's older Silhouette implant. Patients implanted with Dynesys showed a 52 percent treatment success rate after two years, compared with 40 percent for Silhouette.

But panelists questioned the durability of the device beyond that time frame.

"I'm worried about these screws having to last a lifetime," said panelist Dr. Edward Hanley of Carolinas Medical Center.

Panelists said the Dynesys has potential as spine-stabilizing device, but would require a revamped study to better identify the ideal patient population.

The FDA's review of the Dynesys implant was unusual in that it raised questions about whether company payments to physicians conducting the trial may have influenced the results.

More than half of the patients in the trial were treated at medical centers that reported more than $100,000 in payments from the company, according to the FDA's review. While there was a relationship between the payments and whether patients achieved success with the device, the connection was not statistically significant. Panelists said the connection was likely due to chance.

But FDA regulators said companies should expect to see increasing scrutiny of financial payments as part of product reviews. The FDA cited increasing interest from Congress in ties between device makers and surgeons.

Sen. Charles Grassley, R-Iowa, is investigating device maker Medtronic Inc.'s consulting relationships with surgeons. The Minneapolis-based giant is a leading manufacturer of spinal repair products.

Copyright 2009 Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.